The overall objective of the proposed research is to define the cellular mechanisms controlling the assembly and distribution of microtubules and other cytoskeletal proteins for the processes of cell division and neurite differentiation. Studies will employ clonal lines of cultured neuroblastoma cells in which in vivo patterns of microtubule utilization during neurite outgrowth and mitotic spindle formation can be coordinately investigated. Using a radioimmunoassay with antisera specific for total tubulin or polymeric forms, the size and distribution of the microtubule protein pool will be assessed with respect to the assembly of microtubules. In vitro assays will be used to quantitate the assembly properties of neuroblastoma extracts derived from various differentiated states, and experiments on specific neuroblastoma microtubule-associated proteins will be extended to determine the effect of these species on the assembly reaction, and their intracellular location. Biochemical characterization of subunit modifications and nucleating sites which may be involved in regulation of monomer-polymer distribution will also be undertaken, and compared with analyses on the synthesis and turnover of tubulin during differentiation. These biochemical studies will be correlated with morphological observations to identify the cellular changes in tubule distribution important in the processes of cell division and differentiation.